There are many environments where a device that is battery powered is used. In these types of devices (and others) it is common that power management issues are taken into consideration. Such devices include many cellular applications such as for telephony or automotive applications.
In particular circumstance the devices may include wireless local area network (WLAN) chip sets to enable a user to receive services such as voice and video over internet protocol (V2IP).
Historically, WLAN chip sets have been designed predominately for the PC environment. In these circumstances the primary objective has been about data throughput and power consumption is not generally a big consideration. This had led chip manufactures to embed data rate control mechanisms into WLAN chips to optimise the data throughput for the user.
Another power consumption minimisation technique has been to reduce the number of transmitted WLAN packets for a duplex burst from 6 to 4, and then switch off the terminal between WLAN transmissions. This has been adopted by the IEEE 802.11e standard, but does not solve all the problems for V2IP or VoIP over WLAN.
Low power link adaptation has also been proposed by first adjusting data rate to maximise this and then adjusting transmitted power control both for a targeted packet error rate (PER). As data rate maximisation is the overriding objective, power control is often insufficient. This method is based on achieving the highest possible data rates and is not necessarily the most suitable for V2IP or any application which requires a reasonably low throughput.
Another approach teaches monitoring the medium occupancy to select the optimal data rate for specific power consumption. The data-rate is adapted for the WLAN traffic by estimating the WLAN traffic based on the average contention window, or the number of past collisions or the proportion of time the channel was busy during previous frame transmissions. But for V2IP or VoIP application, the transmission rate is low (˜50 transmissions/s) and the transmission duration (relative to the transmission interval) is also low. Thus the traffic may have changed significantly between last transmissions and the next transmissions. This makes this method of estimating the WLAN traffic very unreliable and is thus not a reliable metrics.
If metrics used to estimate the available bandwidth include the contention window of past transmissions for a V2IP or VoIP applications, it is an estimate of the WLAN traffic of the previous 20 ms slots, not of the latest 20 ms slot (just before trying to get access to the channel) and so again is unreliable.
The main drawbacks of the identified prior art include:                1. The reduction in power consumption at different data rates to transmit the same quantity of information with the same radio frequency (RF) propagation conditions is not linear and thus the best data rates to not mean low power consumption.        2. As the nature of V2IP or VoIP transmission medium is typically a radio channel which changes very quickly, propagation conditions can change faster than transmission rate. This severely effects the estimation time for metrics in the link adaptation algorithm making it effectively useless as convergence may never occur.        3. The above mechanisms to estimate the WLAN traffic are well suited for a relatively high loaded WLAN network or when the device attempts to transmit a data packet often. But for applications of low throughput, it is not efficient (for the above explained reasons).        
Finally WLAN power amplifier (PA) bias control has been proposed as a low power consumption solution for WLAN chip sets by Intersil. In this proposal PA bias is adapted to input RF power to maintain a required back-off for modulation types such as OFDM or CCK. The PA bias is kept the same and is not dynamically adjusted.
One object of the present invention is to overcome at least some of the problems of prior art methods and systems.